1. Field of the Invention
The present invention concerns a toothed belt, the belt being constituted by an annular body of elastomeric or similar material in which a structure resistant to tensile stress is embedded. The toothed belt being further characterized by the fact that one face of said annular body has a toothing of elastomeric material.
2. Prior Art
Several types of toothed belts that fit the general description given above are already well known. In general, toothed belts are used in conjunction with at least two toothed pulleys to form a transmission. In all the previously known types of toothed belts, the contours of the toothed belt's teeth are conjugate to the contours of the toothed pulley's teeth. In fact, in a toothed belt and toothed pulleys transmission, the movement is transmitted by a meshing between the toothed belt's teeth and the toothed pulleys' teeth which is similar to the meshing seen with metallic driving gears. However, with a toothed belt and toothed pulleys transmission, in contrast to metallic driving gears wherein all the components of the driving gears are rigid, one of the components of the transmission, namely the toothed belt, is made of an elastomeric material and a deformability which is much greater than that of the other components, namely the toothed pulleys.
The difference in deformability between the toothed belt and the toothed pulleys, and more precisely between the teeth of the toothed belt and the teeth of the toothed pulleys, causes sliding to occur between the teeth of the transmission components when the pressure existing between them is high. Consequently, the toothed belt's teeth are subject to a great deal or wear. In order to avoid and try to limit this wear of the toothed belt's teeth, different contours of the belt's teeth have been studied and proposed in an attempt to reduce sliding between the transmission components. Particular elastomeric compounds have been studied in order to obtain a maximum hardness of the toothed belt's teeth without excessively limiting the flexibility of the toothed belt as a whole.
In spite of the above-mentioned artifices, the problem of wear of the teeth of toothed belts has not been satisfactorily resolved by the previously known designs for toothed belts. Furthermore, because of the great deformability of the teeth of a toothed belt, which are made of an elastomeric material, with respect to the deformability of the metallic teeth of the toothed pulleys, the stresses on the teeth when in a meshed state between a toothed belt and a toothed pulley varies during the movement of the transmission. More particularly, the maximum stress on a tooth of a toothed belt occurs when said tooth begins to be inserted into a groove of the driving toothed pulley. The greatest sliding between the teeth of the belt and those of the pulley also occurs at this time.
Once the insertion of a tooth of the toothed belt into the groove of the driving toothed pulley has occured, the stress on said tooth decreases while the tooth moves together with the driving toothed pulley until the tooth of the toothed belt leaves the toothed pulley. Again, because of this variation of stresses on the tooth of the toothed belt, settling movements of the tooth of the toothed belt within the groove of the toothed pulley occur, and these movements cause further sliding with consequent wear. The settling movements also generate vibrations in the toothed belt and in the transmission which result in the production of noises as well as a further reduction in the lifetime of the toothed belt.